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Climate
Climates encompass the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elements in a given region over a long period of time. Climate can be contrasted to weather, which is the present condition of these same elements and their variations over periods up to two weeks. The climate of a location is affected by its latitude, terrain, and altitude, as well as nearby water bodies and their currents. Climates can be classified according to the average and the typical ranges of different variables, most commonly temperature and precipitation. The most commonly used classification scheme was originally developed by Wladimir Köppen. The Thornthwaite system,C. W. Thornthwaite, "An Approach Toward a Rational Classification of Climate", Geographical Review, 38:55-94, 1948 in use since 1948, incorporates evapotranspiration in addition to temperature and precipitation information and is used in studying animal species diversity and potential impacts of climate changes. The Bergeron and Spatial Synoptic Classification systems focus on the origin of air masses that define the climate of a region. Paleoclimatology is the study of ancient climates. Since direct observations of climate are not available before the 19th century, paleoclimates are inferred from proxy variables that include non-biotic evidence such as sediments found in lake beds and ice cores, and biotic evidence such as tree rings and coral. Climate models are mathematical models of past, present and future climates. Climate change may occur over long and short timescales from a variety of factors; recent warming is discussed in global warming. Definition Climate (from Ancient Greek klima, meaning inclination) is commonly defined as the weather averaged over a long period of time. The standard averaging period is 30 years, but other periods may be used depending on the purpose. Climate also includes statistics other than the average, such as the magnitudes of day-to-day or year-to-year variations. The Intergovernmental Panel on Climate Change (IPCC) glossary definition is: The difference between climate and weather is usefully summarized by the popular phrase "Climate is what you expect, weather is what you get."National Weather Service Office Tucson, Arizona. Main page. Retrieved on 2007-06-01. Over historical time spans there are a number of nearly constant variables that determine climate, including latitude, altitude, proportion of land to water, and proximity to oceans and mountains. These change only over periods of millions of years due to processes such as plate tectonics. Other climate determinants are more dynamic: for example, the thermohaline circulation of the ocean leads to a 5 °C (9 °F) warming of the northern Atlantic ocean compared to other ocean basins.Stefan Rahmstorf. The Thermohaline Ocean Circulation: A Brief Fact Sheet. Retrieved on 2008-05-02. Other ocean currents redistribute heat between land and water on a more regional scale. The density and type of vegetation coverage affects solar heat absorption,Gertjan de Werk and Karel Mulder. Heat Absorption Cooling For Sustainable Air Conditioning of Households. Retrieved on 2008-05-02. water retention, and rainfall on a regional level. Alterations in the quantity of atmospheric greenhouse gases determines the amount of solar energy retained by the planet, leading to global warming or global cooling. The variables which determine climate are numerous and the interactions complex, but there is general agreement that the broad outlines are understood, at least insofar as the determinants of historical climate change are concerned. Climate classification There are several ways to classify climates into similar regimes. Originally, climes were defined in Ancient Greece to describe the weather depending upon a location's latitude. Modern climate classification methods can be broadly divided into genetic methods, which focus on the causes of climate, and empiric methods, which focus on the effects of climate. Examples of genetic classification include methods based on the relative frequency of different air mass types or locations within synoptic weather disturbances. Examples of empiric classifications include climate zones defined by plant hardiness,United States National Arboretum. USDA Plant Hardiness Zone Map. Retrieved on 2008-03-09 evapotranspiration, or more generally the Köppen climate classification which was originally designed to identify the climates associated with certain biomes. A common shortcoming of these classification schemes is that they produce distinct boundaries between the zones they define, rather than the gradual transition of climate properties more common in nature. Bergeron and Spatial Synoptic The most generic classification is that involving the concept of air masses. The Bergeron classification is the most widely accepted form of air mass classification. Air mass classification involves three letters. The first letter describes its moisture properties, with c used for continental air masses (dry) and m for maritime air masses (moist). The second letter describes the thermal characteristic of its source region: T for tropical, P for polar, A for Arctic or Antarctic, M for monsoon, E for equatorial, and S for superior air (dry air formed by significant downward motion in the atmosphere). The third letter is used to designate the stability of the atmosphere. If the air mass is colder than the ground below it, it is labeled k. If the air mass is warmer than the ground below it, it is labeled w. While air mass identification was originally used in weather forecasting during the 1950s, climatologists began to establish synoptic climatologies based on this idea in 1973. Based upon the Bergeron classification scheme is the Spatial Synoptic Classification system (SSC). There are six categories within the SSC scheme: Dry Polar (similar to continental polar), Dry Moderate (similar to maritime superior), Dry Tropical (similar to continental tropical), Moist Polar (similar to maritime polar), Moist Moderate (a hybrid between maritime polar and maritime tropical), and Moist Tropical (similar to maritime tropical, maritime monsoon, or maritime equatorial).Robert E. Davis, L. Sitka, D. M. Hondula, S. Gawtry, D. Knight, T. Lee, and J. Stenger. J1.10 A preliminary back-trajectory and air mass climatology for the Shenandoah Valley (Formerly J3.16 for Applied Climatology). Retrieved on 2008-05-21. Köppen The Köppen classification depends on average monthly values of temperature and precipitation. The most commonly used form of the Köppen classification has five primary types labeled A through E. These primary types are A, tropical; B, dry; C, mild mid-latitude; D, cold mid-latitude; and E, polar. The five primary classifications can be further divided into secondary classifications such as rain forest, monsoon, tropical savanna, humid subtropical, humid continental, oceanic climate, Mediterranean climate, steppe, subarctic climate, tundra, polar ice cap, and desert. Rain forests are characterized by high rainfall, with definitions setting minimum normal annual rainfall between and . Mean monthly temperatures exceed during all months of the year.Susan Woodward. Tropical Broadleaf Evergreen Forest: The Rainforest. Retrieved on 2008-03-14. A monsoon is a seasonal prevailing wind which lasts for several months, ushering in a region's rainy season. Regions within North America, South America, Sub-Saharan Africa, Australia and East Asia are monsoon regimes.International Committee of the Third Workshop on Monsoons. The Global Monsoon System: Research and Forecast. Retrieved on 2008-03-16. A tropical savanna is a grassland biome located in semi-arid to semi-humid climate regions of subtropical and tropical latitudes, with average temperatures remain at or above convert 18C/F year round and rainfall between 750mm/in and convert 1270mm/in a year. They are widespread on Africa, and are also found in India, the northern parts of South America, Malaysia, and Australia.Susan Woodward. Tropical Savannas. Retrieved on 2008-03-16. The humid subtropical climate zone where winter rainfall (and sometimes snowfall) is associated with large storms that the westerlies steer from west to east. Most summer rainfall occurs during thunderstorms and from occasional tropical cyclones. Humid subtropical climates lie on the east side continents, roughly between latitudes 20° and 40° degrees away from the equator.Michael Ritter. Humid Subtropical Climate. Retrieved on 2008-03-16. A humid continental climate is marked by variable weather patterns and a large seasonal temperature variance. Places with more than three months of average daily temperatures above convert 10C/F and a coldest month temperature below and which do not meet the criteria for an arid or semiarid climate, are classified as continental. An oceanic climate is typically found along the west coasts at the middle latitudes of all the world's continents, and in southeastern Australia, and is accompanied by plentiful precipitation year round.Climate. Oceanic Climate. Retrieved on 2008-04-15. The Mediterranean climate regime resembles the climate of the lands in the Mediterranean Basin, parts of western North America, parts of Western and South Australia, in southwestern South Africa and in parts of central Chile. The climate is characterized by hot, dry summers and cool, wet winters.Michael Ritter. Mediterranean or Dry Summer Subtropical Climate. Retrieved on 2008-04-15. A steppe is a dry grassland with an annual temperature range in the summer of up to and during the winter down to convert -40C/F}}.Blue Planet Biomes. Steppe Climate. Retrieved on 2008-04-15. A subarctic climate has little precipitation,Michael Ritter. Subarctic Climate. Retrieved on 2008-04-16. and monthly temperatures which are above convert 10 C/F for one to three months of the year, with permafrost in large parts of the area due to the cold winters. Winters within subarctic climates usually include up to six months of temperatures averaging below .Susan Woodward. Taiga or Boreal Forest. Retrieved on 2008-06-06. Tundra occurs in the far Northern Hemisphere, north of the taiga belt, including vast areas of northern Russia and Canada. A polar ice cap, or polar ice sheet, is a high-latitude region of a planet or moon that is covered in ice. Ice caps form because high-latitude regions receive less energy in the form of solar radiation from the sun than equatorial regions, resulting in lower surface temperatures.Michael Ritter. Ice Cap Climate. Retrieved on 2008-03-16. A desert is a landscape form or region that receives very little precipitation. Deserts usually have a large diurnal and seasonal temperature range, with high daytime temperatures (in summer up to 45 °C or 113 °F), and low night-time temperatures (in winter down to 0 °C; 32 °F) due to extremely low humidity. Many deserts are formed by rain shadows, as mountains block the path of moisture and precipitation to the desert.San Diego State University. Introduction to Arid Regions: A Self-Paced Tutorial. Retrieved on 2008-04-16. Thornthwaite Devised by the American climatologist and geographer C. W. Thornthwaite, this climate classification method monitors the soil water budget using the concept of evapotranspiration.Glossary of Meteorology. Thornethwaite Moisture Index. Retrieved on 2008-05-21. It monitors the portion of total precipitation used to nourish vegetation over a certain area. It uses indices such as a humidity index and an aridity index to determine an area's moisture regime based upon its average temperature, average rainfall, and average vegetation type.Eric Green. Foundations of Expansive Clay Soil. Retrieved on 2008-05-21. The lower the value of the index in any given area, the drier the area is. The moisture classification includes climatic classes with descriptors such as hyperhumid, humid, subhumid, subarid, semi-arid (values of -20 to -40), and arid (values below -40).Istituto Agronomico per l'Otremare. 3 Land Resources. Retrieved on 2008-05-21. Humid regions experience more precipitation than evaporation each year, while arid regions experience greater evaporation than precipitation on an annual basis. A total of 33 percent of the Earth's landmass is considered either arid of semi-arid, including southwest North America, southwest South America, most of northern and a small part of southern Africa, southwest and portions of eastern Asia, as well as much of Australia. Studies suggest that precipitation effectiveness (PE) within the Thornthwaite moisture index is overestimated in the summer and underestimated in the winter. This index can be effectively used to determine the number of herbivore and mammal species numbers within a given area. The index is also used in studies of climate change.Gregory J. McCabe and David M. Wolock. Trends and temperature sensitivity of moisture conditions in the conterminous United States. Retrieved on 2008-05-21. Thermal classifications within the Thornthwaite scheme include microthermal, mesothermal, and megathermal regimes. A microthermal climate is one of low annual mean temperatures, generally between 0C/F and 14C/F}} which experiences short summers and has a potential evaporation between 14cm/in and 43cm/in. A mesothermal climate lacks persistent heat or persistent cold, with potential evaporation between and 114cm/in. A megathermal climate is one with persistent high temperatures and abundant rainfall, with potential annual evaporation in excess of 114cm/in. Record Modern Details of the modern climate record are known through the taking of measurements from such weather instruments as thermometers, barometers, and anemometers during the past few centuries. The instruments used to study weather conditions over the modern time scale, their known error, their immediate environment, and their exposure have changed over the years, which must be considered when studying the climate of centuries past.Spencer Weart. The Modern Temperature Trend. Retrieved on 2007-06-01. Paleoclimatology Paleoclimatology is the study of past climate over a great period of the Earth's history. It uses evidence from ice sheets, tree rings, sediments, coral, and rocks to determine the past state of the climate. It demonstrates periods of stability and periods of change and can indicate whether changes follow patterns such as regular cycles.National Oceanic and Atmospheric Administration. NOAA Paleoclimatology. Retrieved on 2007-06-01. Climate change Climate change is the variation in global or regional climates over time. It reflects changes in the variability or average state of the atmosphere over time scales ranging from decades to millions of years. These changes can be caused by processes internal to the Earth, external forces (e.g. variations in sunlight intensity) or, more recently, human activities.Arctic Climatology and Meteorology. Climate change. Retrieved on 2008-05-19. In recent usage, especially in the context of environmental policy, the term "climate change" often refers only to changes in modern climate, including the rise in average surface temperature known as global warming. In some cases, the term is also used with a presumption of human causation, as in the United Nations Framework Convention on Climate Change (UNFCCC). The UNFCCC uses "climate variability" for non-human caused variations. Earth has undergone periodic climate shifts in the past, including four major ice ages. These consisting of glacial periods where conditions are colder than normal, separated by interglacial periods. The accumulation of snow and ice during a glacial period increases the surface albedo, reflecting more of the Sun's energy into space and maintaining a lower atmospheric temperature. Increases in greenhouse gases, such as by volcanic activity, can increase the global temperature and produce an interglacial. Suggested causes of ice age periods include the positions of the continents, variations in the Earth's orbit, changes in the solar output, and vulcanism.Illinois State Museum (2002). Ice Ages. Retrieved on 2007-05-15. Climate models Climate models use quantitative methods to simulate the interactions of the atmosphere,Eric Maisonnave. Climate Variability. Retrieved on 2008-05-02. oceans, land surface and ice. They are used for a variety of purposes from study of the dynamics of the weather and climate system to projections of future climate. All climate models balance, or very nearly balance, incoming energy as short wave (including visible) electromagnetic radiation to the earth with outgoing energy as long wave (infrared) electromagnetic radiation from the earth. Any imbalance results in a change in the average temperature of the earth. The most talked-about applications of these models in recent years have been their use to infer the consequences of increasing greenhouse gases in the atmosphere, primarily carbon dioxide (see greenhouse gas). These models predict an upward trend in the global mean surface temperature, with the most rapid increase in temperature being projected for the higher latitudes of the Northern Hemisphere. Models can range from relatively simple to quite complex: * Simple radiant heat transfer model that treats the earth as a single point and averages outgoing energy * this can be expanded vertically (radiative-convective models), or horizontally * finally, (coupled) atmosphere–ocean–sea ice global climate models discretise and solve the full equations for mass and energy transfer and radiant exchange.Climateprediction.net. Modelling the climate. Retrieved on 2008-05-02. See also * Atmosphere * Climate Prediction Center * Ecosystem * Effect of sun angle on climate * Greenhouse effect * List of climate scientists * Microclimate * National Climatic Data Center * Outline of meteorology * Solar variation * Temperature extreme * Tropical marine climate * Weather References External links * NOAA Climate Services Portal * IGBP Climate-change Index * The Economics of Climate-based Data NOAA Economics * AgClimate IFAS * Climate Models and modeling groups * Climate Prediction Project * WorldClimate * ESPERE Climate Encyclopaedia * Climate index and mode information regarding the Arctic * A current view of the Bering Sea Ecosystem and Climate * Climate: Data and charts for world and US locations * MIL-HDBK-310, Global Climate Data U.S. Department of Defense Data on natural environmental starting points for engineering analyses to derive environmental design criteria * ClimateDiagrams.com Climate diagrams for over 3 000 weather stations and different climate periods from around the world. Users can create their own diagrams with their own data. * IPCC Data Distribution Centre Climate data and guidance on its use. Category:Basic meteorological concepts and phenomena Category:Climate Category:Modern Category:Ecology